Army cadets and military hardware crossed Kiev's Maidan, or Independence Square, as thousands rallied in an emotional show of strength aimed at boosting morale in the strife-torn nation.

Crowds of Ukrainians, many sporting the national colours of blue and yellow, sang the ex-Soviets state's anthem as the flag was raised.

"I am convinced that the battle for Ukraine, for independence, will be our success," Poroshenko told the crowds in a speech ahead of the parade.

"War has come to us from over the horizon where it was never expected," he said, referring to Russia.

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"In the 21st century, in the centre of Europe, there is a flagrant attempt to breach the border of a sovereign state without declaring war," he said. "It is as if the world has returned to the 1930s, the eve of World War II."

Poroshenko pledged to allocate 40 billion hryvnias ($3 billion, 2.3 billion euros) to its cash-strapped army over the next three years in what he called "only the modest beginning" in the rebirth of the Ukrainian military.

The money will be used to purchase warplanes, warships and helicopters, he said.

- Demonstration of unity -

Crowds, many people wearing traditional embroidered shirts or flower wreaths, densely packed the Maidan and surrounding streets for the first time since the pro-European rallies in the winter that eventually toppled former leader Viktor Yanukovych.

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"It is a demonstration of the unity and independence of Ukraine," said Oleksandr Kaplya, a Ukrainian flag peeking out of his shirt pocket. "We want to show the world that we are one."

It was the first military parade in Kiev in five years, and some said it helped boost the nation's spirits as the Ukrainian army is engaged in a bloody conflict in the east of the country.

"In wartime there were always parades... We need this to lift our military morale," said Roman Kovalchuk, who had travelled to the capital with his wife and friends from southern Ukraine for the occasion.

- Hospital hit in Donetsk -

But while Kiev was gripped by patriotic fervour, fierce clashes continued to ravage the industrial east with mortar fire hitting a hospital in the main rebel hub of Donetsk.

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In the insurgent stronghold meanwhile pro-Russian separatists threatened an event of their own to ridicule the celebrations in Kiev by parading imprisoned Ukrainian soldiers.

On central Lenin square, rebels showcased what they said was military hardware captured from Kiev's army, including artillery guns and armoured vehicles.

A shell hit a hospital in central Donetsk in the early hours of Sunday, damaging a morgue and two other buildings and sending staff and patients to a basement shelter. No one was hurt.

"We heard explosions at 6:30 am, windows broke and doctors told us to leave our rooms to go down here," said one young man in the basement of the surgery ward, who added that he was a Ukrainian soldier injured earlier in the week and now awaiting a prisoner swap.

Donetsk, a city of a million people before the conflict tore through it, has increasingly seen fighting in the streets. On Saturday shelling attacks killed six civilians in residential neighbourhoods, including a child.

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- Putin talks -

Kiev's conflict with the pro-Russian rebels in the separatist regions of Lugansk and Donetsk has claimed more than 2,200 lives since April, and increasingly moved into populated areas in recent weeks as the army surrounds separatist strongholds.

The pro-Western government of Ukraine blames Russia for stoking the insurgency and accuses Moscow of sending in weapons and personnel through parts of the frontier controlled by the rebels -- allegations that Russia hotly denies.

Poroshenko is under pressure ahead of a meeting with Russia's President Vladimir Putin and EU officials in Minsk on Tuesday, where the two are expected to try to take a step toward resolving the bloody conflict.

Earlier this week Moscow set off alarm bells by driving in a convoy of more than 200 trucks in a unilateral aid mission to war-torn Lugansk, where people had been without power or communication for three weeks.

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Kiev slammed the Russian gambit as a "direct invasion" and said its border officials were kept away from checking the contents of most lorries amid fears the convoy would help bolster the rebels.

International monitors said Saturday that the trucks had all returned to Russian territory, but Kiev accused them of looting valuable military equipment from a factory and smuggling it from the country.